My company has had this problem in the past, and there are a couple things
you can do.
First: Go into File|Setup, and make sure the IP address is 0.0.0.0
Second: Be sure and add an init string for their modem. Many times
this will fix your problem, as well as increase the users
performance. Also, NEVER set a baud rate at 14,400 or 28,800.
Set it to 19,200, 38,400, or 57,600. The best thing to do is
to start at the lowest, and work your way up. If it stops working
then you know the modem isn't working at well that speed, and go
down a notch.
Third: If all else fails, reinstall Trumpet Winsock. I know that this
sounds strange, but trust me, we have over 2000 users, and we
have gotten this down. Try the first two steps first, if that
doesn't help, do this one, and most likely you will be working
without any problems!